Manufacture of high wet strength paper



Patented Mar. 24, 953

I MANUFACTURE OF PAP William F. Fowler, 'Jr., and Donald R. Spear, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application June 17-, 1950,

" Serial No. 168,858

9 'Claims.

This application relates to the manufacture of paperespecially adapted for photographic purposes by. means of the use therein of a sizingaid, a'polymeric'hydrosol and aprec-ipitant.

Ordinarily paper is sized to resist penetration of liquids therein and to give the paper a certain amount of body. Also for certain purposes, such as? in the photographic art, it is desirable that the paper have a substantial wet strength due to the fact that it is immersed in aqueous baths of vari-.

ous types. The sizing of the paper at the present time ordinarily involves the precipitation in the mixing chest of stearic acid (or its aluminum salts) from a solution of sodium stearate in alkalinewater by the addition of aluminum sulphate or the like thereto. Recently aluminum chloride has been suggested for this purpose.

To impart high wet strength to the paper in the process of being prepared, water soluble ureaformaldehyde resins or melamine-formaldehyde resins have been added to the pulp slurry after the Jordaning operation and prior to the dispensing of the pulp on to the wire of the paper machine. Although this method of preparing high wet strength paper has been found to be satisfac of styrene-acrylate resins in the preparation of the paper.

. We have found that by adding to a paper pulp while in suspension a composition of a water soluble salt of l-pimaric acid-maleic anhydride adduct (or other sizing aid), a water soluble styrene-acrylate resin, and an aluminum salt of a monobasic acid and preparing paper therefrom,

t'ory in some instances, in other instances it has been found that the resins added impart undesirable characteristics thereto, particularly where the prevalence of even a trace of formaldehyde: cannot be tolerated. Also the preparation of sized high wet strength papers in this fashion has. involved several operations and a large quantity of'eiipensive equipment. Otherj methods of fincreasingthe wet strength of paper have been proposed. For instance,

latices of various types have been suggested as suitable forthis purpose. Many of thesemateii'alsf have been. found to be unstable in the presence of ultraviolet light and also contain sulfur which is active photographically and would be especially undesirable in the case of photographic use. Hydrosols of polyvinyl acetate have been suggested both as coating compositions for paper and use in tub sizing operation. This resin, however; is not sufiicientlyhydrophobic to be useful asasizing agent..-

One object of our invention is to provide a method for use in the preparation of paper which simultaneously sizes and increases the wet strength thereof as well as maintaining the desirable dry strength. Another object of our invention is to provide a method of preparing high quality photographic raw stock. A still further object of our invention is to provide a method for preparing high wet strength paper by means that a product is obtained having good sized properties, high wet strength, and good resistance herein a sizing aid may be either an alkali metal salt, an ammonium salt, or an amine salt thereof.

The sodium salt may be prepared as follows: 98 parts of'sodium hydroxide pellets were dissolved in 1000 parts of distilled waterand the solution was heated on a steam bath with stirring. When the temperature of the solution was about C., 325 parts of the l-pimarie acid-maleic anhydride adduct previously ground to a finepowder were added. Almost immediate solution occurred to produce a dark brown fluid containing 30.2 per cent solids. This solution was cooled to room temperature and a portion of it was diluted with distilled water to produce the desired concentration. We have found that the water soluble salts of abietic acid and of hydrogenated abietic acid are also efiective assizing aids in preparing paper in accordancewith our invention.

The styrene-acrylate resin for use in preparing paper inaccordance with our invention may be prepared as follows: 0.63 part of potassium per-' sulfate and 1.25 parts of sodiumlauryl sulfate were dissolved in 500 parts ofdistilled water and were placed in-a vessel equipped with a dropping funnel, a-mechanical stirrer, and a reflux condenser. The solution was heated with steam while stirring with the dropwise addition of a mixture consisting'of 63 parts of washed styrene and 63 parts of washedn-butyl acrylate. .Polymerization to produce a milky-appearing sol was essentially complete in about 45 minutes. The mixture was then heated for two hours in order to insure complete polymerization. It was then cooled and stored readyfor use. Instead of butyl acrylate, other acrylates may be employed in preparing th resin for use in our composition. Some of the acrylates which may be employed are n-butyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyLacrylate, n-amyl acrylate, n-amyl methacrylate The aluminum saltof a monobasic acid which is most useful in th processes described herein isaluminum chloride. It is desirable to obtain the optimum effect from th resins employed that the percentage of the styrene in the styrene-acrylate copolymer be at least 40% and not greater than 75%, although both sides of the paper simultaneously over a circular area of approximately 1 inch diameter. A potential is applied that allows 200 ma. of current to flow when no paper sample is present.

percentages outside of this range would give 5 When a paper sample is mounted in the blocks, resins having an eifeetiveness though more limthe. tim in se onds is noted from the moment ited. the electrolyte is first brought in contact with It is desirable in using the various ingredients the paper sample until 160 milliamperes of curof the composition. which we. have described that 7 rent flows through the paper sample. ose ingredients be added in the form of their 10 The results on testing the hand sheet preaqueous solutions or sols as the case may be. For pared were as follows: instance, the sizing aid is conveniently employed as a 5 per cent aqueous solution, whereas the con- Valley penetration secs 39 centration of the resin in the hydrosol may be as Cobb size grams 0.156 much as 20% or higher (40%). We have found Wet strength p. s. i 8% that where the materials are used in proportions. equivalent to the following that the best results Example II.-A series of runs were made in are obtained: 60-70 parts of dry pulp, 1-5 parts a similar. manner as in Example I, the composisizing aid, 1-20 parts of the styrene-acrylate tions' used and the results obtained being as resin, 2-20 parts of aluminum chloride. follows:

Vane? Wet U. v. Composition Pegggra- Cobb Size Strength Exp. Unexp. Dill.

2.5 ml. 10% quinoline H01 5 ml. 5% sodium salt of l-pimarie acidmaleic anhydride adduct 40 0.149 8% 82.5 80.2 2.3 10ml. hydrosol of styrene-acrylate resin. ml. aluminum chloride solution (14%) 5 mlhsoidigm 111; otf l-pimarlc acid maleic an y n ea uc 10 ml. hydrosol of styiene-acrylate resin. 36 mm 9% o 1 9 mi. afilucminulmfclrloride solutliofin (14%)-. C I .m y oso o s yrene-acrya eresm... '0111 etc. ene- 25 ml, aluminum chloride solution.(l4%).. 1 tra ion. p 4% 5 25 ml. 10% quinoline H01 10ml. hydrosolof styrene-acrylate resin... 1 ..do 3% 83.0 80.1 2.9 25 ml. aluminum chloride solution (14%)-. 2.5 ml. 131% quinoline H Cl material.irrrrieifirri 1 a? m 25 ml. aluminum chloride solution (14%)..

The following examples illustrate the use of our invention in the preparation of paper sheets, 40

the following all involving the preparation of hand sheets to show the effectiveness of our method.

Example I.Three liters of 2%,% suspension of a-cellulose pulp which. had been beaten for one hour were stirred while the following chemicals were added: 5 ml. of 5% solution of trisodium salt of l-pimaric acid-maleic anhydride adduct, 10 ml. of the hydrosol of styrene-n-butyl acrylate such as described above, 25 ml. of 14 per cent of aluminum chloride in water. Also 1.7 ml. of 10% solution of quinoline hydrochloride in water were added, although this addition is optional. After thoroughly mixing and diluting the pulp; slurry to the desired consistency, hand sheets approximately eight inches square and weighing 2.50 grams were prepared on a Noble and Wood hand sheet device. The sheets were dried by passing over a rotary drum dryer at The ultraviolet reversion test (last two columns). was run by subjecting examples to ultraviolet light covering the /2 of the sample with material to prevent exposure while maintaining a temperature of C. The exposure time recorded is the time required to revert a standard pulp sample 3 /z%, the reversion being the difference in brightness between the exposed and unexposed parts. Brightness is measured on a recording spectrophotometer at 456 m wave length.

" for the comparison as'specified above.

Example III .-A hydrosol was prepared similar to that described previously, except that it contained the following monomeric mixture: 61 parts of styrene,.61 parts of .butylacrylate and 6.2 parts 210 F. over the course of. three minutes. of 50% aqueous acryli? acid- W this The hand sheets so prepared were tested for drosol was employed prepanng sheets of degree of Sizing by means, of the valley pene paper, the results obtained were as-fcllows: tration test and by the Cobb size test (TAPPI Valley enetration 33 standard No. T441-m-45). Wet strength was 65 Cobb size 0.166 evaluated by soaking a hand sheet in distilled Wet strength 1 3% water for two hours at room temperature and r v measuring the bursting strength on the. Minden ggg gg g fig gj g fg g i g $g Paper tester in Pmmds'per square inchparts of commercial gradaabietic acid were The Valley penetration recorded in Seconds is ground to a line powder and slowly heated to 210 measured asfollows: A two-inch square sample Q with 9 parts 0f maleic anhydride wh o pap r t bev tested is mounted between two the temperature had reached 100 0., themass wooden blocks that have b drilled to allow melted. At.160' 0., it began to darken slightly a solution consisting of 516 ml. of distilled water, but the temperature was. slowly raised to 210 24g; ofNaCl and 60ml. of 'glycerine to contact Crover theperiodcf'an hour."After-cooling Mal material in the following proportions:

5 ml. 5 ammonium salt of adduct 10 ml. 20% styrene butyl methacrylate copolymer hydrosol 25 ml.'14% aluminum chloride solution The results obtained were as follows;

Valley penetration 92 Cobb size 0.138 Wet strength 8 Example IV.-Various styrene-acrylate resins were prepared using the following proportions:

Parts Parts Number Styrene Acrylate Ester Acrylate 60. l 65. 9 56. 5 69. 5 53. 2 72. 8 50. 3 75. 7 47. 5 78. 5 81. 4 44. 6 78. 48. 0 75. 0 51. 0 72. 0 54.0 69. 0 2-Butoxyethyl 57. 0

Hand sheets were prepared from these various styrene-acrylate resins by beating three liters of of 2%% pulp suspension for one hour while adding the following chemicals:

ml. of 5% salt of 1-pimaric acid-maleic anhydride adduct }added as a 10 ml. of hydrosol of styrene-acrylate copolymer mixture. ml. of 14% aqueous aluminum chloride.

The paper sheet was prepared as described in Example I. These sheets were tested for physical properties and the results are summarized as follows, using the designations of acrylate esters to.

indicate the sheets tested.

. -In preparing paper sheets, some times it is desirable to increase the Mullen value (TAPPI T403-m-41) or dry bursting strength thereof. In accordance with inventions it may be desirable to. add such material. Some ofthe materials which have been found to be useful in this connection are starch used in the proportion of 26% based on the dry sheet of the pulp, methacrylamide used in a proportion of 5 -20% based on the weight of the resin employed, or locust bean gum. An illustration of the preparation of hand sheets including starch is as follows:

Example V.Six liters of a 2 4% suspension of a-cellulose pulp which had been beaten for one hour were also mixed with the following chemicals:

1. A volume of a 4 /2% aqueous solution of corn starch prepared by heatinga slurry of corn starch and cold water to 170 F. as indicated in the table. I 2. 10 ml. of a 5% of the sodium salt l-pimaric acid-maleic anhydride adduct.

3. 20 ml. of 20% hydrosol of styrene-n-butyl ac- V rylate copolymer. 4. 10 ml. of 14% aqueous aluminum chloride.

These mixtures were then formed into sheets in the manner indicated herein. The various sheets containing different amounts of starch were tested for physical properties with the results as follows:

. Sizing Volume Starch Solution Added Mullen ggg Valley Cobb None s7 9% 47 .131 33 ml 40 10% 47 The sizing method of our invention has been operated using various concentrations of the chemicals which are employed, and it has been found that the concentrations used of the various chemicals in their aqueous solutions or suspensions may be varied depending on the convenience in carrying on this operation.

Example VI .--A copolymer latex was prepared as follows: 19.9 g. of freshly recrystallized methacrylamide, 1.26 g. of sodium lauryl sulfate, and 0.63 g. of potassium persulfate were dissolved in 500 ml. of hot tap water, placed in a, reaction vessel equipped with refluxing apparatus, wherein the mass was stirred and heated on a steam bath while a mixture containing 41.5 g. of washed n-butyl acrylate and 64.9 g. of washed styrene were added dropwise with stirring At the end of one hour of steam heating, the resultant hydrosol was cooled to room temperature. The resulting product was tested in paper sheets using therewith the sodium salt of pimaric, acid-maleic anhydride adduct, and aluminum chloride as described herein. The results obtained were as follows:

Mullen 37 Wet strength 9%. Valley penetration 37 Cobb .131

Valley Sizing Aid Mullen Wet Pene- Cobb Strength nation Trisodium maleo pimarate 3 comparison 7 13 87 1 Sodium abietate 35 12% 75 1%; Sodium tetrahydroabietate.-. 37 10% 76 139 We have found that it is better to add the chemicals to the pulp after the pulp suspension has been subjected to a moderate beating. It is preferable: that the pulp bebeaten only so as to have a slowness of 10-50 seconds (Williams) as excessive beating reduces the sizing values and wet strengths of the-paper prepared therefrom. We have further found that the order of adding the various chemicals to the suspension isnot critical with the exception that for best results the aluminum salt should not be contacted with either the resin or the sizing aid alone, but these two materials should be together when so contacted. For instance, if the aluminum salt is added first to the pulp, then the sizing aid and the resin must be added as a mixture. If the sizing aid or the resin is to be added first to the pulp,'then it isv necessary to add the other, either separately or as their mixture, before adding the aluminum salt thereto.

,We have further found that in preparing the resin hydrosols for use in our process; that the surface-active agent which is employed in that preparation should be of the anionic type and that it'should not be more than 2 per cent and preferably 1 per cent or less (but at least 0.1%)

based on the monomer content of the mass. :Somesurface-active agents which may be employed are sodium higher alcohol sulfates, sodium saltsv of higher fatty acids, sulfated fatty alcohols, and the like.

What we claim and desire to secure by Le ters Patent of the U. S. is:

l. A composition useful for imparting high wet strength to paper comprising iparts of the sodium salt of a pimaric aoid-maleio anhydride adduct, 1-20 parts of a styrene-butyl acrylate resin in which the styrene is 40-75% thereof, and'Z-ZO parts of aluminum chloride.

2. A high wet strength paper essentially consisting of paper pulp containing therein a composition comprising 1-5 parts of a sizing aid selected from the group consisting of the water solublesalts of pimaric acid-maleic anhydride 'adduct, the water soluble salts ofabietic acid,

and the-water soluble salts of hydrogenated abietic acid, 1-20 parts of a styrene-alkyi acrylate resinin which the alkyl has 3-6 carbon atoms and the styrene is 40-75% thereof, and 2-20 parts of aluminum chloride.

3. A high wet strength paper essentially consisting of paper pulp containing therein a composition comprising l-5 parts of an alkali metal salt of pimaric acid-maleic anhydride adduct,

l-ZO parts of a styrene-alkyl acrylate resin, the alkyl having 3-6 carbon atoms and the styrene heing 40-75% thereof, and 2-20 parts of alumim1m chloride.

A. composition useful for imparting high wet strength to paper comprising l-5 parts of asizing; aid. selected from the group consisting 5. A composition, useful for imparting high wet strength to. paper comprising 1-5 parts'of an alkali metal salt of. pimaric acid-maleic anhydride adduct, l-ZO parts of a styrene-alkyl acrylate resin, the alkyl having 3-6 carbon atoms-and the styrene being 40-75% thereof, and 2-20 parts of aluminum chloride.

6. A composition, useful for impartinghigh wet strength to paper comprising 1-5 parts, of an alkali metal saltof abietic acid. 1-20 parts of a styrene-alkyl acrylate resin, the alkylhaving 3-6 carbon atoms and the, styrene, being 40-75% thereof, and 2-20 parts of aluminum chloride.

7. A composition useful for imparting high wet strength to paper comprising 1-5 parts of analkali metal salt of hydrogenated abietic acid, 1-20 parts of styrene-alkyl acrylate resin, the alkyl having 3-6 carbon atoms and the styrene being 40-75% thereof, and 2-20 parts of aluminum chloride.

8.1In a method of preparing high wet strength paper, a stepwhich comprises incorporating into the suspension of paperpulp employed in preparing the paper a composition comprising 1-5 parts of an alkali metal salt. of pimaric acid.- maleic anhydride adduct, 1-20parts of a styrenealkyl acrylate resin, the alkyl having.3-6.carb0n atoms and thestyrene being 40-75% thereof, and 2-20 parts of aluminum chloride.

l 9. In a. method of preparing'high' wet strength paper, the step which comprises incorporating into the suspension of paper pulp employed in preparing the paper a composition comprisin 1-5 parts of the, sodium salt of a pimarioacid-maleic anhydride adduct, l-20 parts of a styrene-butyl acryiate resin in which the styrene is 40-75% thereof, and. 2-20 parts of aluminum chloride.

WILLIAM F. FOWLER, JR. DONALD R. SPEAR.

REFERENCES CITED The following references are of record, in the file of this patent:

UNITED STATES" PATENTS Number Name Date 1,943,975 Lathrop et al Jan. 16, 1934 2,081,389 Borglin May 25, 1937 2,216,845 Larson Oct. 8, 1940 2,301,998 Berstein et'al. Nov. 17,1942 2,315,675 Trommsdorf .,Apr. 6, 1943 2,338,839 'Coss Jan. 11, 1944 2,394,289 Boughton Feb. 5, 1946 OTHER REFERENCES Taft: Paper Trade Journal, March 6, 1941, pp. 34-37.

Dreshfeld; Paper Trade Journal, July 17, 19.41, page 40.

Collins et 211.: Paper Trade Journal, September 25, 1941, pages 9 1-99.

Wilson et al.: Paper Trade Journal, November 18, 1943, page 32.

Rivise: Paper Trade Journal, March 21, 1929, page 63-. 

6. A COMPOSITION USEFUL FOR IMPARTING HIGH WET STRENGTH TO PAPER COMPRISING 1-5 PARTS OF AN ALKALI METAL SALT OF ABIETIC ACID, 1-20 PARTS OF A STYRENE-ALKYL ACRYLATE RESIN, THE ALKYL HAVING 3-6 CARBON ATOMS AND THE STYRENE BEING 40-75% THEREOF, AND 2-20 PARTS OF ALUMINUM CHLORIDE. 